1. Field of the Invention
This invention relates to improved hydraulic actuator systems for marine inboard/outboard drive units.
2. Description of Related Art
Hydraulic rams are used to provide power steering for marine inboard/outboard drive units, such as those sold under the trade mark Volvo. In one type of unit an hydraulic ram has an actuator rod connected to the tiller arm of the inboard/outboard unit and extends to one side thereof. The operation of the ram is governed by a servo mounted on top of the ram which includes a spool valve which is spring loaded to a center, closed position. A mounting tube extends outwardly from the spool valve parallel to the actuator rod of the ram. When the tube is displaced in one direction, the spool valve opens to allow hydraulic fluid to enter the ram so the ram is activated in the same direction as the tube. The ram moves until the ram has been displaced the same distance as the mounting tube. The same thing occurs when the mounting tube is displaced in the opposite direction.
Movement of the mounting tube can be accomplished by a system of cables which extend forwardly from the drive unit to the helm of the boat. However, operation of the steering system is improved, and the need for cables eliminated, by using an hydraulic actuator to the move the mounting tube of the spool valve. Hydraulic lines then connect the drive unit to the helm which is connected to an hydraulic pump. One type of hydraulic actuator system is sold by Volvo in their Kit No. 1140585-9. The hydraulic actuator in this system is clamped to a pair of spaced-apart brackets which are connected to the mounting tube on opposite sides of the servo. The clamping of the cylinder is accomplished by tightening a pair of bolts on the clamps of each of the brackets. This method of mounting the actuator is disadvantageous for a number of reasons. First, the system relies on friction to hold the actuator in place. If the bolts become loose, then the actuator can slip axially, causing steering disfunction. This may not become apparent until the loading on the mounts is greater than usual, such as occurs if the power steering ram should fail. The power steering actuator can provide enough power to steer the boat, with considerably increased steering effort, should the ram fail. However, the loading on the clamps is considerably increased and the cylinder may slip under such an extreme emergency condition.
Furthermore, over-tightening the bolts is also undesirable. This can deform the cylinder of the actuator, causing the piston to stick slightly as it passes the deformed section of the cylinder adjacent the clamp. This gives an undesirable "lumpy" feeling to the steering and may cause oversteering when the piston frees itself after moving past the deformed portion of the cylinder.
As a result, there is a need to provide an improved hydraulic actuator mounting system which is less subject to malfunction if a few bolts are under-tightened or over-tightened as sometimes occurs for bolts or nuts which are easibly accessible to installers or repairmen.